The objective of this research is to evaluate the decrease in cancer risk resulting from the removal of plutonium and other transuranium elements from the body by chelation therapy. Although hundreds of papers have been written on the removal of radioactivity by chelation, only three studies have attempted a direct evaluation of its effect on cancer incidence, and these involved relatively brief periods of chelation. We now have 17 chelated beagles that were injected with 241Am or 239Pu in 1973-1976. Without chelation treatment nearly all these dogs would be destind to die of bone cancer, but with protracted therapy with ZnDTPA or CaDTPA the skeletal burden has been decreased by an average factor of 5, and it is possible that many of these dogs will live normal lifespans free of radionuclide-induced cancer. We are most anxious to continue the follow up of these animals so that the residual risks can be evaluated. In addition, we propose to evaluate the effect of brief, intermediate and prolonged chelation therapy on the reduction of 239Pu-induced cancers in mice. The information from these studies should be especially valuable to physicians who treat persons accidentally contaminated with transuranium elements and, hopefully, will reveal mechanisms accounting for this protection.